Neurological disorders are often caused by neural impulses failing to reach their natural destination in otherwise functional body systems. Local nerves and muscles may function, but, for various reasons, injury, stroke, or other cause, the stimulating nerve signals do not reach their natural destination. For example, paraplegics and quadraplegics have intact nerves and muscles and only lack the brain to nerve link, which stimulates the muscles into action.
Prosthetic devices have been used for some time to provide electrical stimulation to excite muscle, nerve or other cells. Such devices have ranged in size and complexity from large, bulky systems feeding electrical pulses by conductors passing through the skin, to small, implanted stimulators which are controlled through telemetry signals, such as are discussed in U.S. Pat. No. 4,524,774, Apparatus and Method for the Stimulation of a Human Muscle, invented by Jurges Hildebrandt, issued Jun. 25, 1985. Other devices have comprised a centrally-implanted stimulator package sending stimulation signals to a multitude of distant target sites.
Complications, including the possibility of infection, arise in the use of stimulators which have conductors extending through the skin. On the other hand, in the use of implanted stimulators, difficulties arise in providing suitable, operable stimulators which are small in size and have the capability to receive and store sufficient energy and control information to satisfactorily operate them without direct connection.
The device of the invention uses a source of electrical energy outside the skin, modulated by desired control information, to selectively control and drive numerous, small stimulators disposed at various locations within the body. Thus, for example, a desired, progressive muscular stimulation may be achieved through the successive or simultaneous stimulation of numerous stimulators, directed by a single source of information and energy outside the body.
The construction of a microstimulator presents problems of its own, which are not encountered in the construction of larger-sized biomedical appliances. The extremely small size involves problems and solutions of a different nature than are ordinarily involved. The appropriate design of a suitable, small stimulator, a microstimulator, which can be easily implanted, such as by expulsion through a hypodermic needle, is difficult to achieve. Notwithstanding the small size and required shape, the microstimulator structure must contain means for receiving and storing sufficient energy to provide the desired stimulating pulses, as well as electronics which provides control of the characteristics desired of the stimulating pulse.